The function of a tightly bound zinc ion at the active site of E. Coli DNA polymerase I is being studied with chelating agents and ligands which are potent inhibitors of the enzyme. The chelating agents are fluorescent derivatives of 1,10-phenanthroline which yields characteristic fluorimetric changes upon coordination to ionic zinc and interaction with the enzyme. Reversal of spectroscopic signals obtained with the enzyme by substrates will suggest possible catalytic functions of the metal ion. Several novel inhibitors of DNA polymerase I have been discovered and their site of action is being explored. Of particular interest is a derivative of fluorescein which inhibits at concentrations of 10 to the minus 8th power M. The ligand binding topography and subunit structure of the acetylcholine receptor protein is being explored using a photoaffinity label with a comparable structure to decamethonium. Initial studies have revealed specific modification of the receptor protein with this label upon photolysis. Fluorescent ligands of the acetylcholine receptor protein are also being used to study the conformational properties of the receptor protein in its soluble and membrane-bound form.